The ear canal 10 (FIG. 2) is generally narrow and tortuous and is approximately 26 millimeters (mm) long from the canal aperture 11 to the tympanic membrane 17 (eardrum). The lateral part is flexible and referred to as the cartilaginous canal due to the underlying cartilaginous tissue 16 beneath the skin 15. The medial part, proximal to the tympanic membrane, is rigid and referred to as the bony region due to the underlying bone tissue 13. A characteristic first bend occurs roughly at the aperture 11 of the ear canal. A second characteristic bend 18 occurs roughly at the bony-cartilaginous junction and separates the cartilaginous region and the bony region. The dimensions and contours of the ear canal vary significantly among individuals, but are generally narrow with little space for accommodating miniaturized components within. The ear canal is generally sensitive to touch and pressure, particularly in the deeper region which can readily experience discomfort, abrasion and trauma with pressure and rigid contact. Abrasion of the skin inside the ear canal due to hearing aid use is common and generally limits insertions to the lateral (outer) portions of the ear canal.
Amplified sound is preferably delivered inside the ear canal. Deep insertion of a speaker in the ear canal is advantageous for several electroacoustic reasons including reduction of the acoustic occlusion effect, improved energy efficiency, reduced distortion, reduced receiver vibrations, and improved high frequency response. Hearing devices can be fit entirely or partially inside the ear canal, including In-The-Ear (ITE), Behind-The-Ear (BTE), Receiver-In-the Canal (RIC), In-The-Canal (ITC) and Completely-In-the-Canal (CIC), as well as extended wear deep canal invisible types recently available to consumers. Hearing devices, or a receiver assembly associated with a hearing device, generally requires acoustic sealing to seal amplified sound in the residual volume of the ear canal and prevent leakage that leads to oscillations, commonly known as “feedback”. An earpiece can function as an acoustic seal, or alternatively as a retention piece for a hearing device inserted in the ear canal
Custom hearing devices generally rely on custom housing, or a custom ear mold, according to an impression made of an individual ear canal. Alternatively, universal designs with generic shapes are also known in the art. They rely on generic-shape rigid housing or a compliant earpiece functioning as a seal and/or a retainer, eliminating the need for custom fabrication. For example, the hearing aid industry offers an assortment of “dome” type compliant earpieces that connect with a speaker assembly for RIC devices. These earpieces are replaceable when soiled or degraded after use inside the ear canal. Due to the space constraints inside the ear canal, securing a removable earpiece assembly to the hearing device presents a challenge to hearing aid designers in terms of space efficiency, comfort, ease of replacement, security of attachment and cost. One major consideration is minimizing rigid structures associated with an earpiece while maximizing the compliant part to fit inside the ear canal without discomfort or trauma. For this reason among others, replaceable earpiece assemblies are generally limited to larger types of hearing devices such as BTE and RIC, rather than canal hearing devices.